Depression is common in teenagers, with 11 percent being diagnosed by age 18, and many more having depressive symptoms. Social and academic stress can trigger depression, and rates of depression tend to peak in adolescence around the age of 16.

It doesn't help that stressed-out teens often fall into hopelessness, says David Yeager, an assistant professor of psychology at the University of Texas at Austin. "When kids have hard things happen to them, they think it'll be like that way into the future."

Researchers started noticing back in the 1980s that many teens felt that social and personality traits were immutable — that someone who is once a loser is always a loser.

So what if we could convince kids that things can change for the better — would that help mitigate the high rates of depression? Yeager tested that out. The results of his latest study, published Monday in Clinical Psychological Science, suggests that it does.

The study divided 600 ninth-graders into two groups. Half participated in a brief intervention program designed to help them understand that people and circumstances can change. These teenagers were shown several articles, including one about brain plasticity, and another about how neither bullies nor victims of bullying are intrinsically bad.

"We didn't want to say something to teenagers that wasn't believable," Yeager says. "We just wanted to inject some doubt into that problematic world view that people couldn't change."

The students also read advice from older students reassuring them that high school gets better, and they were asked to draw from their own experience and write about how personalities can change.

Nine months later, the researchers checked up on all the students. Among those who didn't participate in the intervention, rates of depression symptoms such as feeling constantly sad and feeling unmotivated rose from 18 percent to 25 percent — about what the researchers expected, Yeager says. The group that participated in this intervention showed no increase in depressive symptoms, even if they said they were bullied.

Of course this is a fairly small study. And the intervention doesn't treat clinical depression. At most, it helps kids who may be prone to depression cope better.

"I would say the research is at an early stage," says Gregory Walton, an assistant professor of psychology at Stanford University who wasn't involved in the study. "But this is a fairly promising start."

For one, the intervention is pretty easy to start and scale up, Walton says.

And Yeager's previous research indicates that the intervention also helps with aggression and general health. Other researchers have found that similar interventions help teens do better academically.

Like teens, many adults tend to feel that people and circumstances don't change, Walton says. "But adolescence might be a good window of opportunity to target that belief."

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